The present invention relates to a flasher type fish sonar for displaying fish and a bottom of the water by luminosity of a luminous body in a window of a display board.
In a prior art flasher type fish sonar, a circular window is formed in the periphery of a display board provided on the front of a case, a light emitting body, mounted on a rotary disk, is arranged opposite the window, the rotary first is rotated by a motor and a sensor is fixed on the "0" position of the display board.
In this flasher display, when the light emitting body is detected by the sensor, output signals from a control means are applied to an oscillating circuit, oscillating signals from the oscillating circuit are applied to an ultrasonic transducer, and ultrasonic waves from the ultrasonic transducer are emitted to the water.
When reflected ultrasonic waves are received by the ultrasonic transducer and are converted to the reflected signals amplified by a receiving circuit and are converted to digital reflected signals by an analogue to a digital converter, the digital signals are transmitted from the control means to the light emitting body of the display apparatus whereby positions of fish and the bottom of the water are displayed on the window of the display apparatus.
In such a flasher type fish sonar, because "0" graduation is fixed on the upper portion of the display board, each of the depth graduations are shown on the display board by right-handed rotation, and the graduation of the deepest portion is shown near the "0" graduation. The luminosity of the second reflected signal of the bottom is displayed on the portion of the display board which is higher than the lowest portion of the display board. Thus it is hard to distinguish the luminosity of the "0" graduation and the luminosity of the second reflected signal. Also, in the deep range, because the light of the bottom position is displayed on the portion of the display board which is above the position of the fish, it is hard to distinguish the luminosity of the "0" graduation and the luminosity of the bottom.